The present invention relates to a multiple aperture device for low-frequency line arrays. Specifically, the device converts the surface area of a single 12″ woofer into the acoustic equivalent of multiple smaller transducers through multiple apertures for coherent summation when more than one element (woofer) is used in an array.
A line array is a loudspeaker system that is made up of a number of usually identical loudspeaker elements mounted in a line and fed in phase, to create a near-line source of sound. The distance between adjacent drivers is close enough that they constructively interfere with each other to send sound waves farther than traditional horn loudspeakers, and with a more evenly distributed sound output pattern. Each element in a line array must act as a “point source” over its operating bandwidth to achieve coherent summation of their wave fronts. In order to achieve coherent summation, the center-to-center spacing of these point sources cannot exceed one-half wavelength of the highest intended operating frequency. To satisfy the required low-frequency range and output it is often desirable to use a 12″ diameter transducer (woofer). When arrayed in a line, the 12″ diameter and subsequent 12″ minimum center-to-center spacing means the woofers will only sum coherently to 600 Hz. This would require a very low crossover point for transitioning from the low-frequency transducer to the high-frequency device which is not possible for the devices being used.
Previous inventions used simple obstruction devices that provided only limited control of the vertical radiation pattern at the expense of uniformity of coverage in the horizontal plane.